Conventionally, impact tools such as a hammer and a hammer drill are able to apply an impact force to a tool bit. Patent Literature 1 describes an example of the impact tool. The impact tool described in Patent Literature 1 has a hollow casing, an electric motor provided in the inside of the casing, an intermediate shaft to which a rotational force of the electric motor is transmitted via a first gear train, a hollow cylinder to which a rotational force of the intermediate shaft is transmitted via a second gear train, and a tool bit attached to the cylinder.
In addition, a piston which is movable in a center line direction of the cylinder is provided. The piston has a cylindrical shape, and an impact element is inserted in the inside of the piston. Moreover, in the inside of the cylinder, an intermediate element serving as an impact force transmitting member is provided. In addition, the piston, the intermediate element and the tool bit are disposed coaxially, and the intermediate element is disposed between the piston and the tool bit in a direction along the center line. Then, a pneumatic chamber is formed between a bottom part of the piston and the impact element.
On the other hand, a driving force conversion mechanism is provided in the inside of the casing. The driving force conversion mechanism converts the rotational force of the intermediate shaft into a reciprocating force of the piston. Moreover, a clutch mechanism is provided in the inside of the casing. The clutch mechanism transmits the driving force of the intermediate shaft to the driving force conversion mechanism or cuts off the driving force based on an operation of a change lever.
In the impact tool described in Patent Literature 1, the rotational force of the electric motor is transmitted to the cylinder via the first gear train, the intermediate shaft and the second gear train, and the cylinder is rotated. The rotational force of the cylinder is transmitted to the tool bit, and the tool bit is rotated. In addition, when the change lever has been operated and the clutch mechanism has been turned-off, the driving force of the intermediate shaft is not transmitted to the piston. Consequently, the impact force is not applied to the impact element.
Meanwhile, when the change lever has been operated and the clutch mechanism has been turned-on, the rotational force of the intermediate shaft is converted into the reciprocating force of the piston by the driving force conversion mechanism. Then, the air pressure in the pneumatic chamber repeats up and down alternately, and the impact force is transmitted to the intermediate element. When the tool bit is pressed against a machining object, since the tool bit and the intermediate element are in contact with each other, the impact force transmitted to the intermediate element is transmitted to the tool bit. In this way, the impact force is applied to the tool bit while the tool bit is being rotated.
On the other hand, grease as a lubricant is enclosed in the inside of the casing, and the grease lubricates lubrication object parts such as the first gear train, the second gear train and the driving force conversion mechanism. In addition, when the use of the impact tool is interrupted or terminated after the operation of the impact tool is finished, the tool bit is made to be separated from the machining object.